1. Field of the Invention
The present invention relates to magnetic powder, a manufacturing method of magnetic powder and bonded magnets. More particularly, the present invention relates to magnetic powder, a manufacturing method of the magnetic powder and a bonded magnet which is produced, for example, using the magnetic powder.
2. Description of the Prior Art
For reduction in size of motors, it is desirable that a magnet has a high magnetic flux density (with the actual permeance) when it is used in the motor. Factors for determining the magnetic flux density of a bonded magnet include magnetization of the magnetic powder and the content of the magnetic powder to be contained in the bonded magnet. Accordingly, when the magnetization of the magnetic powder itself is not sufficiently high, a desired magnetic flux density cannot be obtained unless the content of the magnetic powder in the bonded magnet is raised to an extremely high level.
At present, most of practically used high performance rare-earth bonded magnets are the isotropic bonded magnets which are made using the MQP-B powder manufactured by MQI Inc. as the rare-earth magnetic powder thereof. The isotropic bonded magnets are superior to the anisotropic bonded magnets in the following respect; namely, in the manufacture of the bonded magnet, the manufacturing process can be simplified because no magnetic field orientation is required, and as a result, the rise in the manufacturing cost can be restrained. On the other hand, however, the conventional isotropic bonded magnets represented by those manufactured using the MQP-B powder involve the following problems.
(1) The conventional isotropic bonded magnets do not have a sufficiently high magnetic flux density. Namely, because the magnetic powder that has been used has poor magnetization, the content of the magnetic powder to be contained in the bonded magnet has to be increased. However, the increase in the content of the magnetic powder leads to the deterioration in the moldability of the bonded magnet, so there is a certain limit in this attempt. Moreover, even if the content of the magnetic powder is somehow managed to be increased by changing the molding conditions or the like, there still exists a limit to the obtainable magnetic flux density. For these reasons, it is not possible to reduce the size of the motor by using the conventional isotropic bonded magnets.
(2) Although there are reports concerning nanocomposite magnets having high remanent magnetic flux densities, their coercive forces, on the contrary, are so small that the magnetic flux densities (for the permeance in the actual use) obtainable when they are practically used in motors are very low. Further, these magnets have poor heat stability due to their small coercive forces.
(3) The conventional bonded magnets have low corrosion resistance and heat resistance. Namely, in these magnets, it is necessary to increase the content of the magnetic powder to be contained in the bonded magnet in order to compensate the low magnetic properties (magnetic performance) of the magnetic powder. This means that the density of the bonded magnet becomes extremely high. As a result, the corrosion resistance and heat resistance of the bonded magnet are deteriorated, thus resulting in low reliability.
It is therefore an object of the present invention to provide magnetic powder that can manufacture bonded magnets having excellent magnetic properties and having excellent reliability.
In order to achieve the above object, the present invention is directed to a magnetic powder composed of an alloy composition represented by (R1-aDya)x(Fe1-bCob)100-x-yBy (where R is at least one kind of rare-earth element excepting Dy, x is 7.1-9.9 at %, y is 4.6-8.0 at %, a is 0.02-0.2, and b is 0-0.30), wherein the magnetic powder is constituted from a composite structure having a soft magnetic phase and a hard magnetic phase, and the intrinsic coercive force (HCJ) of the magnetic powder at a room temperature is in the range of 400-750 kA/m.
According to the magnetic powder as described above, it is possible to provide bonded magnets having excellent magnetic properties as well as excellent reliability.
Another aspect of the present invention is also directed to a magnetic powder composed of an alloy composition represented by (R1-aDya)x(Fe1-bCob)100-x-y-zByMz (where R is at least one kind of rare-earth element excepting Dy, M is at least one element selected from Cu, Ga, Si, Sn, In, Ag and Al, x is 7.1-9.9 at %, y is 4.6-8.0 at %, z is equal to or less than 3.0 at % (not including 0), a is 0.02-0.2, and b is 0-0.30), wherein the magnetic powder is constituted from a composite structure having a soft magnetic phase and a hard magnetic phase, and the intrinsic coercive force (HCJ) of the magnetic powder at a room temperature is in the range of 400-760 kA/m.
According to the magnetic powder as described above, it is also possible to provide bonded magnets having excellent magnetic properties as well as excellent reliability.
In the present invention, it is preferred that the magnetic powder is obtained by milling a melt spun ribbon. This makes it possible to further improve magnetic properties, especially coercive force and the like.
Further, it is also preferred that the thickness of the melt spun ribbon is 10-40xcexcm. This also makes it possible to obtain bonded magnets having especially excellent magnetic properties.
Preferably, the melt spun ribbon is obtained by colliding a molten alloy of a magnetic material onto a circumferential surface of a cooling roll which is rotating to cool and then solidify it. According to this method, it is possible to obtain microstructure (fine crystal grains) with relative ease, so that the magnetic properties can be further improved.
In this case, it is preferred that the cooling roll includes a roll base made of a metal or an alloy and an outer surface layer provided on an outer peripheral portion of the roll base to constitute the circumferential surface, in which the outer surface layer of the cooling roll has a heat conductivity lower than the heat conductivity of the roll base. This makes it possible to quench the puddle of the magnetic material with an adequate cooling rate, so that it becomes possible to obtain magnets having especially excellent magnetic properties.
In this case, it is preferred that the outer surface layer of the cooling roll is formed of a ceramics. This also makes it possible to quench the puddle of the magnetic material with an adequate cooling rate, so that it becomes possible to obtain magnets having especially excellent magnetic properties. Further, the durability of the cooling roll is also improved.
In the present invention, it is preferred that the R comprises rare-earth elements mainly containing Nd and/or Pr. This makes it possible to improve saturation magnetization of the hard phase of the composite structure (in particular, nanocomposite structure), and thereby the coercive force is further enhanced.
Further, it is also preferred that said R includes Pr and its ratio with respect to the total mass of said R is 5-75%. This makes it possible to improve the coercive force and rectangularity without lowering the remanent magnetic flux density.
In the present invention, it is also preferred that the magnetic powder is constituted from a composite structure having a soft magnetic phase and a hard magnetic phase. This makes it possible to improve magnetizability as well as heat resistance (heat stability) so that changes in the magnetic properties with the elapse of time become small.
Further, it is also preferred that the magnetic powder is subjected to a heat treatment for at least once during the manufacturing process or after its manufacturing. According to this, homogeneity (uniformity) of the structure can be obtained and influence of stress introduced by the milling process can be removed, thereby enabling to further improve the magnetic properties of the bonded magnet.
In the magnetic powders described above, it is preferred that the mean crystal grain size is 5-50 nm. This makes it possible to obtain magnets having excellent magnetic properties, especially excellent coercive force and rectangularity.
Further, in the magnetic powders described above, it is also preferred that the average particle size lies in the range of 0.5-150 xcexcm. This makes it possible to further improve the magnetic properties. Further, when the magnetic powder is used in manufacturing bonded magnets, it is possible to obtain bonded magnets having a high content of the magnetic powder and having excellent magnetic properties.
Further, the present invention is directed to a method of manufacturing a magnetic powder, in which a melt spun ribbon is obtained by colliding a molten alloy of a magnetic material onto a circumferential surface of a cooling roll which is being rotating to cool and then solidify it, and then thus obtained melt spun ribbon is milled to obtain the magnetic powder, wherein the magnetic powder is composed of an alloy composition represented by (R1-aDya)x(Fe1-bCob)100-x-yBy (where R is at least one kind of rare-earth element excepting Dy, x is 7.1-9.9 at %, y is 4.6-8.0 at %, a is 0.02-0.2, and b is 0-0.30), wherein the magnetic powder is constituted from a composite structure having a soft magnetic phase and a hard magnetic phase, and the intrinsic coercive force (HCJ) of the magnetic powder at a room temperature is in the range of 400-750 kA/m.
According to this method, it is possible to provide magnetic powder having excellent magnetic properties and having excellent reliability.
Further, the present invention is also directed to a method of manufacturing a magnetic powder, in which a melt spun ribbon is obtained by colliding a molten alloy of a magnetic material onto a circumferential surface of a cooling roll which is being rotating to cool and then solidify it, and then thus obtained melt spun ribbon is milled to obtain the magnetic powder, wherein the magnetic powder composed of an alloy composition represented by (R1-aDya)x(Fe1-bCob)100-x-y-zByMz (where R is at least one kind of rare-earth element excepting Dy, M is at least one element selected from Cu, Ga, Si, Sn, In, Ag and Al, x is 7.1-9.9 at %, y is 4.6-8.0 at %, z is equal to or less than 3.0 at % (excepting 0), a is 0.02-0.2, and b is 0-0.30), wherein the magnetic powder is constituted from a composite structure having a soft magnetic phase and a hard magnetic phase, and the intrinsic coercive force (HCJ) of the magnetic powder at a room temperature is in the range of 400-760 kA/m.
According to this method, it is also possible to provide magnetic powder having excellent magnetic properties and having excellent reliability.
Furthermore, the present invention is directed to a bonded magnet formed by binding a magnetic powder with a binding resin, wherein the magnetic powder is composed of an alloy composition represented by (R1-aDya)x(Fe1-bCob)100-x-yBy (where R is at least one kind of rare-earth element excepting Dy, x is 7.1-9.9 at %, y is 4.6-8.0 at %, a is 0.02-0.2, and b is 0-0.30), and the magnetic powder is constituted from a composite structure having a soft magnetic phase and a hard magnetic phase, and the intrinsic coercive force (HCJ) of the magnetic powder at a room temperature is in the range of 400-750 kA/m.
According to the bonded magnet described above, it is possible to obtain bonded magnets having excellent magnetic properties and having excellent reliability.
Further, the present invention is directed to a bonded magnet formed by binding a magnetic powder with a binding resin, wherein the magnetic powder is composed of an alloy composition represented by (R1-aDya)x(Fe1-bCob)100-x-y-zByMz (where R is at least one kind of rare-earth element excepting Dy, M is at least one element selected from Cu, Ga, Si, Sn, In, Ag and Al, x is 7.1-9.9 at %, y is 4.6-8.0 at %, z is equal to or less than 3.0 at % (excepting 0), a is 0.02-0.2, and b is 0-0.30), and the magnetic powder is constituted from a composite structure having a soft magnetic phase and a hard magnetic phase, and the intrinsic coercive force (HCJ) of the bonded magnet at a room temperature is in the range of 400-760 kA/m.
According to the bonded magnet described above, it is also possible to obtain bonded magnets having excellent magnetic properties and having excellent reliability.
In these bonded magnets, it is preferred that the intrinsic coercive force (HCJ) of the bonded magnet at a room temperature is in the range of 400-750 kA/m. This makes it possible to provide bonded magnets having excellent heat resistance and magnetizability as well as sufficient magnetic flux density.
Further, in these bonded magnets, it is also preferred that the maximum magnetic energy product (BH)max[kJ/m3] is 50 kJ/m3. This makes it possible to obtain small sized high performance motors.
Furthermore, in these bonded magnets, it is also preferred that when the density of the bonded magnet is xcfx81[Mg/m3], the maximum magnetic energy product (BH)max[kJ/m3] at a room temperature satisfies the relationship represented by the formula (BH)max/xcfx812[xc3x9710xe2x88x929Jxc2x7m3/g2]xe2x89xa72.10. This makes it possible to obtain especially excellent magnetic properties.
Moreover, it is also preferred that when the density of the isotropic bonded magnet is xcfx81[Mg/m3], the remanent magnetic flux density Br[T] at a room temperature satisfies the relationship represented by the formula of Br/xcfx81[xc3x9710xe2x88x926Txc2x7m3/g]xe2x89xa70.125. This also makes it possible to obtain especially excellent magnetic properties.
Moreover, it is also preferred that the absolute value of the irreversible flux loss (initial flux loss) is less than 6.2%. This makes it possible to obtain bonded magnets having especially excellent heat resistance (heat stability).
These and other objects, structures and advantages of the present invention will be apparent from the following detailed description of the invention and the examples thereof which proceeds with reference to the accompanying drawings.